Research over the past decade has revealed an important role for chromatin-modifying and chromatin-remodeling enzymes in coordinated regulation of the circadian clock. This is not unexpected given that a core element in eukaryotic circadian clocks is a transcriptional negative feedback loop. Chromatin functions to organize eukaryotic DNA, but also creates a barrier for transcription. This necessitates a role for chromatin remodeling in maintaining circadian rhythms. In this proposal, I am seeking to further define the modifications that occur at the Neurospora central clock gene frequency and examine the role of heterochromatin in clock and clock-controlled gene expression. Experiments discussed herein will examine this problem using a combined approach. In Specific Aim 1, I propose to isolate the central clock gene frequency in its native chromatin state and identify chromatin modification by Mass Spectrometry. In Specific Aim 2, I will examine how the KMT1 DIM-5 is directed to chromatin and the role of H3K9 methylation in clock and clock controlled gene expression. In Specific Aim 3, I examine if there are circadian clock-regulated changes to genome structure. Data obtained in these aims will be compared and contrasted to understand the relationship between genome structure and clock regulated gene expression. Overall, this proposal will further our understanding of how chromatin structural changes effects circadian regulated gene expression. PUBLIC HEALTH RELEVANCE: The biological clock plays a critical role in normal cell physiology and metabolism. Moreover, it is now widely recognized as an important factor in human health. Understanding the molecular mechanisms in model organisms presents a wonderful opportunity to further define the role of chromatin in clock function.